March is always a zoo at Phoenix Sky Harbor International Airport thanks to spring training, spring break and NASCAR, but this year's crowds were record-breaking.

Monthly statistics released Friday show 4.38 million passengers traveled through Sky Harbor's three terminals in March. That's up 2.3 percent from March 2017, and is the most passengers the airport has handled in a month.

Sky Harbor's biggest tenants, American and Southwest airlines, each saw notable increases in passengers. Together the two dominate the airport, accounting for more than 80 percent of Sky Harbor's passengers.